The present invention addresses the problem of accidental scratching of medical personnel and/or laboratory personnel by hypodermic needles. This problem has become much more serious of late due to the increased presence of the HIV virus and other serious infectious microorganisms. The precausions now required of medical establishments regarding handling and disposal of needles are quite onerous, and even those do not eliminate accidental scratches and/or punctures.
Modern disposable needles are provided with removable and replaceable covers, which offer some protection, but the very acts of removing and replacing such a cover lend themselves to the very kind of accident sought to be prevented. Also, it is a virtual necessity that the needle be left uncovered between filling of the syringe and giving the injection.
Accordingly, a number of efforts have been made, particularly in the last few years, to develop safety mechanisms which can be associated with needles and/or syringes to further reduce the risk. Many of these efforts have involved designs for protective sheaths which can be attached to a needle or a syringe to cover the needle after and/or before its use. However, many of these are relatively bothersome to use and/or do not, respectively, cover the needle and permit uncovering of the needle at all appropriate times.
U.S. Pat. No. 4,664,654 to Strauss and U.S. Pat. No. 4,900,311 to Stern et al. disclose such sheaths. However, both of them require the sheath to be retracted, so as to uncover the needle, and latched into a retracted position prior to using the needle, i.e. inserting it into a vial to take in medication and/or injecting it into a patient. This is unsatisfactory because it is just prior to, during, and immediately after such procedures that the accidental scratches and/or punctures are most likely to occur.
The device disclosed is U.S. Pat. No. 4,973,316 to Dysarz likewise leaves the needle uncovered prior to use, and the pushing of the plunger of the syringe releases a sheath so that it will automatically be extended to cover the needle as that needle is removed from the patient's body. Moreover, since the latch which holds the sheath retracted prior to pushing the plunger is only usable once, and the sheath, when it advances to cover the needle, becomes locked in its extended position, the needle can never be uncovered or used again without destroying the device. Thus, in addition to sharing the general problems above concerning Strauss and Stern et al., the Dysarz device could be triggered into its needle covering mode if the syringe plunger is pushed all the way in prior to taking up medication from a vial, whereupon the sheath would be permanently locked in place and the syringe could not be used to give the injection.
U.S. Pat. No. 4,894,055 to Sudnek does provide a sheath which remains in an extended, needle covering position until it is placed against the patient's body, and the needle projected beyond it and into the patient's body. However, as with Dysarz, as the needle is withdrawn from the patient's body, a spring extends the sheath over the needle and a permanent lock automatically locks the sheath in its extended position. Thus, like Dysarz, Sudnek presents problems in terms of being able to fill the syringe before giving the injection.
U.S. Pat. No. 4,923,447 to Morgan, U.S. Pat. No. 4,966,592 to Burns et al., and U.S. Pat. No. 5,013,301 to Marotta, Jr. et al., all describe devices intended to be operated in much the same manner as those of Strauss and Stern et al. in that it is intended that the sheath be unlatched from an extended position covering the needle, manually retracted, and latched into a retracted position prior to using the needle. If one were to attempt to thwart the prescribed use by unlatching the sheath from its extended position, but not manually retracting it, and attempt to use it somewhat in the manner described by Sudnek, a slight contact with the sheath could inadvertently re-latch the sheath in its extended position. Moreover, Morgan and Burns et al., are more complex structurally than is desirable for an inexpensive disposable syringe combination, and Marotta, Jr. et al., is bothersome in that a separate clip is completely removed to unlock the sheath and must be re-emplaced to relock the sheath in its extended position after use.
U.S. Pat. No. 4,946,446 to Vadher is even more complicated. Its structure and operation is a reminiscent of the sort of ballpoint writing pen in which successive longitudinal pushes on an actuator button or the like alternately extend and retract the writing tip of the pen from a casing. In Vadher, it is the needle which is successively extended and retracted. It is also noted that, whereas many of the prior art devices described above mount a sheath on a syringe. There are a number of reasons why it might be considered preferable to mount the sheath directly to the needle sub-assembly, and Vadher attempts to do this. However, it that context, i.e. in terms of a device intended to be mounted on a needle sub-assembly, the mechanical complexity of Vadher, and most especially the lengthwise dimension required for the working parts, is particularly undesirable and unpractical.
A device known as the "3 cc. Safety-Lok Safety Syringe" and available from Becton Dickinson is believed to be similar to Sudnek and Dysarz in that a sheath which can be advanced to cover a needle after use is then permanently locked in place so that the needle cannot be re-used.
Another commercial system known as the "Monoject System of Safety" and available from Sherwood Medical of Saint Louis Missouri simply provides a large sheath which can be removed from the needle prior to filling and then used as part of a stand in which the needle can be placed until the injection is given, whereafter the sheath is again used to cover the needle for disposal.